1. Field of the Invention
The invention relates to a molding die for forming an optical element with a lens-barrel, in which an optical raw material (or glass raw material) is placed in the lens-barrel set in the molding die and heated and pressurized between a upper die and a lower die and thereby the optical element is integrally formed in the lens-barrel.
2. Description of the Related Art
In recent years, in forming an optical element (or a glass-formed component) by heat softening an optical raw-material (or an optical glass) in a heating furnace and thereafter heating and pressurized it between a upper die and a lower die, a method of manufacturing an optical element with a lens-barrel has been used. In this method, a lens-barrel is set in a molding die comprising a guide die, the upper die and the lower die, and also an optical raw material (or a glass raw material) is placed in the lens-barrel, and the optical raw material is sandwiched, heated and pressurized between the upper die and lower die to cause the optical raw material (or glass material) to flow in the direction of the outer periphery thereof, and thus the outer edge of the optical raw material is caused to tightly join to the inner peripheral surface of the lens-barrel, thereby integrally forming the optical element in the lens barrel (see the gazette of JP-A-4-21528).
FIG. 1 shows a molding die for an optical element with a lens-barrel according to a conventional technology.
A molding die shown in FIG. 1 comprises a guide die 1, a upper die 2 and a lower die 3. Therein, a lens-barrel 10 is placed at a lens-barrel-placing portion 1C provided in the guide die 1, and also an optical raw material 20 placed in the lens-barrel 10 is sandwiched, heated and pressurized between the upper die 2 and lower die 3. Thereby, the transfer surfaces 2A and 3A of the upper die 2 and lower die 3 are transferred to the optical raw material 20 to mold an optically functioning portion, and at the same time, the optical raw material 20 is caused to flow in the direction of the outer periphery thereof, whereby the optical raw material is tightly joined to the inner peripheral surface of the lens barrel 10, thus forming an optical element with a lens barrel.
By the way, in the conventional example shown in FIG. 1, the guide die 1 uses the combination of guide dies 1A and 1B divided in the upper and lower parts. When the formed optical element with a lens barrel is taken out from the guide die 1, conventionally the guide dies 1A and 1B are separated, such that the optical element with a lens barrel placed in the lens-barrel-placing portion 1C is taken out.
When the optical element is formed in the lens barrel 10 placed in the lens-barrel-placing portion 1C as in the molding die of the conventional technology, in order that the position deviation of the lens barrel 10 set in the molding die may cause no optical-axis deviation of the optical element integrally formed, (1) the inside diameter of the lens-barrel-placing portion 1C of the guide die 1 is designed to the outside diameter of the lens-barrel 10, and also (2) the outside diameter of the lower die 3 (upper die 2) is designed to the inside diameter of the guide die 1, or the inside diameter of the guide die 1 is designed to the outside diameter of the lower die 3 (upper die 2).
However, in order to fit the lens-barrel 10 on the outer periphery of the lower die 3 without giving an impact to the lens barrel 10, design looseness is provided between the outside diameter of the lens-barrel 10 and the inside diameter of the lens-barrel-placing portion 1C of the guide die 1 (for example, the inside diameter of the lens-barrel-placing portion is made about 10 μm larger than the outside diameter of the lens barrel) and, at the same time, in order to slide the lower die 3 (upper die 2) in the guide die, design looseness is provided between the outside diameter of the lower die 3 (upper die 2) and the inside diameter of the guide die 1 (for example, the inside diameter of the guide die is made about 10 μm larger than the outside diameters of the upper die and lower die). Due to (1) the looseness between the outside diameter of the lens-barrel 10 and the inside diameter of the lens-barrel-placing portion 1C of the guide die 1 and (2) the looseness between the inside diameter of the guide die 1 and the outside diameter of the lower die 3 (upper die 2), particularly in the case of manufacturing a small optical element with a lens-barrel, the position of the transfer surface 3A of the lower die 3 (the transfer surface 2A of the upper die 2) is deviated with respect to the lens-barrel 10, and thus conventionally an optical-axis deviation occurs in the optical element molded in the lens-barrel 10.
Further, in the molding die of the conventional technology, an optical element placed on the transfer surface 2A of the lower die 3 is integrally formed on the inner peripheral surface of the lens-barrel 10 held by the lens-barrel-placing portion 1C of the guide die 1. For this reason, there is a fear that the axial position deviation of the optical element formed on the inner peripheral surface of the lens barrel 10 may be caused by the looseness between the barrel length of the lens-barrel 10 and the length of the lens-barrel-placing portion 1C.
On the other hand, JP-A-60-129220 discloses a molding die in which the lens-barrel is placed on the lower die. FIG. 2 shows the molding die disclosed by JP-A-60-129220. Therein, by sliding a fitting portion 32 of the lower die 3 and a fitting portion 21 of the upper die 2 in the lens-barrel placed on the bottom 31 of the lower die 3, and adjusting the axial positions of the upper die 2 and the lower die 3 by a spacer 4 provided on the bottom 31,an optical raw material (or a glass material) 20 placed in the lens-barrel is sandwiched, heated and pressurized between the transfer surface 2A of the upper die 2 and the transfer surface 3A of the lower die 3, thereby manufacturing an optical element integrally formed in the lens-barrel. However, in this molding die, the positioning of the center axes of the upper die 2 and the lower die 3, that is, the positioning of the optical axis of the optical element formed in the lens barrel is performed by the contact between the inner peripheral surface of the lens-barrel 10 and the fitting portions 21 and 32 of the upper die 2 and lower die 3. At this time, a large load is imposed on the lens-barrel 10. Particularly in the case of manufacturing a small optical element with a lens-barrel, because the wall of the lens-barrel 10 is thin in thickness, a problem has arisen in terms of the strength of the lens-barrel 10. That is, because of a large load imposed on the lens-barrel 10, there has been problems in terms of accuracy, such as the lens-barrel 10 is deformed and the accurate positioning of the optical element integrally formed in the lens-barrel is prevented by the deformation of the lens-barrel 10.